1. Field of the Invention
The present invention relates generally to an apparatus and method for measuring a distance, and more particularly, to an apparatus and method for measuring a distance by measuring the Time of Arrival (ToA) of a signal.
2. Description of the Related Art
Ubiquitous computing is a concept of building a space in which all entities and objects are intellectualized and connected to an electronic space, and information is exchanged between them by adding a computing function to every physical space and object such as roads, bridges, tunnels, buildings and building walls.
The ubiquitous computing is founded on the basic premise that all computers are connected to one another, are always available to users though invisible to the users, and are integrated into their daily lives. A core infrastructure for realizing this ubiquitous environment, the ubiquitous network is an information communication network that is accessible to anyone irrespective of time and place without any constraints such as communication speed, and can distribute any type of information and content.
Owing to the realization of the ubiquitous network, users can expect to enjoy information communication services freely without many limitations encountered with legacy information communication networks and services. Particularly, a community that goes beyond time and space can be formed by use of the ubiquitous network, and various sensors and the contexts and locations of people and objects can be known through the community.
Ubiquitous computing and the ubiquitous network will create new, diverse services and a ubiquitous location-based application service for locating persons and objects at any time and place. Providing a useful service based on the locations is an important aspect of the ubiquitous environment.
Location awareness technology for acquiring information about the current location of a user is supported with priority in order to realize the ubiquitous computing that autonomously recognizes the situation of a user at any time and place, and provides a service suitable for the situation to the user. Active research is underway on location awareness technology.
Typically, wireless location awareness technologies measure the current location of a wireless device through wireless communications with another wireless device using a wireless signal. Location information permits the efficient use of information acquired through wireless communications over an efficiently configured network.
To improve the accuracy of location awareness in wireless location awareness technologies, accurate detection of the distance between two devices is important. The distance is generally calculated by the ToA of a wireless signal between the two devices.
The ToA of a signal transmitted by the other party is calculated by counting clock pulses.
FIG. 1 is a block diagram of a conventional ToA-based distance measuring apparatus. Referring to FIG. 1, the apparatus includes a first device 13 for transmitting a distance measurement signal and a second device 11 for receiving the distance measurement signal and transmitting a response signal for the distance measurement signal to the first device 13. The first device 13 has a transceiver 101 for transmitting and receiving signals to and from the second device 11, a signal detector 103 for detecting characteristics of a received signal, and a distance calculator 105 for calculating the distance to the second device 11 according to the detected signal characteristics. The signal detector 103 is provided with an original signal detector 107 and a peak detector 109.
In operation, the first device 13 transmits a distance measurement signal to the second device 11. The second device 11 transmits a response signal for the distance measurement signal to the first device 13. The transceiver 101 of the first device 13 is responsible for signal transmission and reception of the first device 13.
The original signal detector 107 of the signal detector 103 determines whether the received response signal is for the transmitted distance measurement signal. If the response signal is for the distance measurement signal, the peak detector 109 detects the peak value of the response signal and the distance calculator 105 calculates the ToA of the response signal based on the peak value.
While the ToA of the response signal is easily calculated in a single-path environment, a plurality of faded response signals can be received from a plurality of paths in a multi-path environment. The multi-path faded signals are received as one overall signal and the earliest of the response signals cannot be found. As a consequence, the second device 13 cannot be accurately located, which will be described in detail with reference to FIGS. 2A and 2B.
FIGS. 2A and 2B illustrate the waveforms of response signals that are detected using a conventional ToA scheme.
Referring to FIG. 2A, in the single-path environment, the ToA of a response signal can be calculated in the distance measuring apparatus illustrated in FIG. 1. However, in the multi-path environment, two or more response signals are generated and are overlapped in time, and thus a single response signal with a wide waveform covering all the multi-path faded response signals is received as illustrated in FIG. 2B. In this case, the earliest response signal cannot be found. If the ToA of the overall response signal is calculated based on its peak value, the difference between the intended earliest response signal and the overall response signal results in a large measurement error.
Although the earliest response signal can be extracted by a Super Resolution (SR) algorithm, a large computation complexity of the SR algorithm makes it difficult to apply to a mobile device.